Cardiovascular disease (CVD) is the single leading cause of death in America. The major underlying pathology contributing to CVD is atherosclerosis. The dynamic nature of atherosclerosis involves remodeling of the blood vessel wall to accommodate for changes in vessel compliance. Initially, this process is adaptive, later it becomes injurious. An important component of vascular remodeling includes the phenotypic modulation of smooth muscle cells (SMCs) in and around the atherosclerotic plaque. SMCs undergo dramatic changes following blood vessel injury; cells proliferate, become invasive, and modify their metabolic properties. The molecular mechanisms underlying SMC behavior are poorly understood. An important characteristic of the pathologic SMC phenotype is the production of proteases that allow for SMC invasion and vessel remodeling. Matrix metalloproteases (MMPs) are a family of endopeptidases that are largely responsible for the degradation of extracellular matrix, and play important roles in vascular remodeling and modulation of SMC behavior. MMP1 is a key player in the process of vascular repair, and is often over-expressed in atherosclerotic plaques. Published data show that MMP1 is an important activator of protease-activated receptor 1 (PAR1). SMCs express high levels of PAR1, and expression is increased in atherosclerotic plaques. The role of PAR1 signaling in SMCs represents an interesting paradox in vascular physiology; the cells only contact the natural activator, thrombin, during times of injury, which raises numerous questions about the role of PAR1 on SMCs. Furthermore, MMP1 and thrombin cleave and activate PAR1 at differing sites, leading to the hypothesis that thrombin and MMP1 differentially activate PAR1 to modulate SMC activity following vascular damage. The long-term goal of this project is to better understand the pathophysiology of maladaptive vascular remodeling. The immediate objective is to investigate the mechanism of a thrombin-MMP1-PAR1 signaling axis in vascular repair. To accomplish these goals, two specific aims have been identified. First, to characterize the role of thrombin- vs MMP1-activated PAR1 signaling in vascular repair, and second, explore the contribution of PAR1 signaling in mouse models of vascular injury. To accomplish aim 1, in vitro assays for proliferation, migration, and invasion will be performed on SMCs utilizing PAR1 and MMP1 agonists/antagonists. Furthermore, we will interrogate the mechanism of thrombin- vs MMP1-activated PAR1 in SMCs. Additionally, the role of a thrombin-MMP1-PAR1 autocrine axis will also be explored. Mouse models of vascular repair will be used to investigate aim 2. Carotid artery wire injury will be performed on PAR1 and MMP1 knock-out mice, and vessels will be analyzed for neointimal lesion formation. Finally, the efficacy of PAR1 targeted pepducins will be tested as therapies for the treatment and prevention of vascular neointimal formation.